The invention relates to a needle bearing with an outer ring terminating on both its ends in a collar, and with bearing needles guided in a cage in axis parallel disposition, as well as with a lubricant reservoir arranged in the bearing.
Such needle bearings as bearings of smallest radial height are generally known and include an outer ring and a needle rim which form together a structural unit. These bearings permit particular cost-efficient rolling contact bearings of high load-carrying capability. The precise guidance of the needle rollers in the cage ensures a reliable operation of such a bearing even at high numbers of revolution (INA-Catalog Nadellager [needle bearing], Zylinderrollenlager [cylindrical roller bearing], p. 306, 1991).
The reservoirs disposed in the bearing and filled with lubricant ensure a reliable lubrication of the bearing over a longer period, thereby increasing the service life.
A drawback is however the limited size of the lubricant reservoirs as a consequence of the small radial structural height. DE 44 41 237 attempted to eliminate this deficiency by providing an additional lubricant reservoir between a collar and the bearing needles. This was realized, for example, by providing the collar about its inner face with axial bulges which are evenly spaced about the circumference so as to form free spaces therebetween for receiving lubricant. Another possibility according to this prior art is implemented by arranging between the collar and the collar of the bearing cage a circular ring which includes at least over a portion of its radial extension elevations which are evenly spaced about the circumference and face the cage, so that free spaces are formed therebetween for receiving lubricant.
These solutions have shortcomings because, on the one hand, the provision of such additional lubricant reservoirs between collar and bearing needles is very complicated, and, on the other hand, the axial dimension of such a bearing is increased.
It is thus an object of the present invention to provide a needle bearing of the afore-stated type with an additional lubricant reservoir which is easy to make and does not enlarge the axial dimension of such a bearing in an undesired manner.
This object is attained in accordance with the invention by forming the lubricant reservoir through a groove disposed in the outer ring and through a middle part of the bearing needles, whereby the diameter of the middle part is reduced in relation to the remaining diameter of the bearing needles.
The manufacture of the groove, which points in the direction of the bearing needles, can be easily integrated in the overall fabrication process of the outer ring so that complicated shaping processes and/or punching of the collars are eliminated. Also an additional manufacture of components for enlarging the grease reservoir is no longer required. In addition, the manufacture of the bearing needles, which have a reduced diameter in mid-section, poses no technical problems. As a consequence of the configuration of the needle bearing in accordance with the invention, the. axial dimension of the needle bearing is not unnecessarily extended as the provision of the lubricant reservoir is accompanied only by a slight restriction of the load-carrying capability. Furthermore, the provision of an enlarged lubricant reservoir results in a lubrication of a bearing of small radial structural height throughout its service life or the periods for re-lubrication can be extended.
Advantageous configurations of the invention are described in the dependent claims set forth hereinafter. In accordance with another feature of the present invention, the groove extends over the entire circumference of the inner surface area of the outer ring or only over a portion thereof. According to another feature of the present invention a seal is disposed between the bearing needles and the collars. Needle bearings, sealed in this manner and typically including lip seals, protect the bearing under operational conditions from dirt or splash water as well as from loss of lubricant. According to another feature of the present invention a collar can be replaced by a closed bottom. Such needle bearings, called needle bushings, seal bearing areas at shaft ends and are suitable for absorbing start-up forces. Furthermore, they represent an effective accident protection when the shaft rotates.
An exemplified embodiment of the invention will now be described in more detail.